This invention relates to a release mechanism which operates underwater and, more particularly, a mechanism which allows the release of ballast from a submersible geophysical exploration unit such as an ocean-bottom seismograph (OBS) permitting the recovery of the device and in the case of the OBS, the recorded data. In recent years, ocean bottom seismographs (devices for measuring vibrations in the earth's crust) have been increasingly utilized in underwater geophysical exploration. In a typical exploratory operation, one or more seismographs are located on the ocean floor to measure artificially generated seismic disturbances. Information gathered by the seismograph is either transmitted directly to the water's surface through appropriate leads for recording or is recorded within the seismograph on appropriate equipment and retrieved from the ocean floor. Positioning and recovery of these devices can be accomplished in shallow waters by divers but this method becomes an expensive if not impossible task in many of the deeper ocean areas where such exploration is now taking place. Cables have been used for positioning and recovery of OBS's and in some cases for the transmission of seismic data to the water's surface, but also have limitations which become more significant as OBS's are placed and operated at increasing depths. Cables are expensive, create turbulence in water flowing around the OBS causing noise which degrades the data being gathered, and may break or be severed resulting in loss of the equipment, data or both. For these reasons, so-called "pop-up" OBS's are increasingly being used in deep water seismic exploration. Pop-up seismographs generally comprise a frame fitted with floats, instruments, power sources and ballast. Released at the ocean's surface, they are allowed to free fall to the ocean floor. Recovery is accomplished by the planned release of ballast which allows the then buoyant assembly to float to the water's surface where it may be retrieved.
In recent years, a variety of ocean bottom seismographs have been constructed and used, each with its own release mechanism. In an article "Ocean Bottom Refraction Seismograph (OBRS)" published in Marine Geophysical Researches 3 (1978), F. Avedik, et al schematized an OBS release mechanism wherein the primary release actuator was a rotary motor operated cam which first released and then forced open a pivoting latching arm freeing the ballast and the secondary actuator was an explosive bolt which when detonated released the assembly by which the pivoting latching arm was secured. An electroplating stainless steel wire release mechanism was described by A. K. Ibrahim, et al at the 46th Annual Society of Exploration Geophysicists meeting of October 24, 1976 in Houston, Tex. The OBS in which that release mechanism was employed was relatively small (weighing approximately 170 pounds) and consisted of a single buoyant glass sphere mounted to a frame by three elastic straps joined together by a piece of stainless steel wire. Release was achieved by passing an electric current through the stainless steel wire causing it to electroplate into solution where exposed to the sea water eventually releasing the glass sphere.
Many of the release mechanisms employed thus far have used explosive bolts as a means of releasing the ballast. Although relatively safe, explosive bolts do, nonetheless represent a danger to personnel working with the OBS prior to its launch as well as during and after its recovery if an unexploded bolt is still present. Redundant means of releasing the buoyant package have been utilized on various OBS's.